1. Field of the Invention
The present invention relates to elastic materials for use in elastic rollers used in electrophotographic apparatuses or electrostatic recording apparatuses such as photocopiers and printers. The present invention further relates to elastic rollers including an elastic layer formed of said elastic materials and electrophotographic apparatuses and electrostatic recording apparatuses incorporating such elastic rollers. Particularly, the present invention relates to developer carriers such as development roller and imaging apparatuses, and more particularly, to a developer carrier for supplying developers to an imaging body retaining a latent image to form a visible image on the imaging body in an imaging apparatus such as photocopiers and laser printers, wherein the developer carrier is capable of preventing formation of contact marks thereon when the developer carrier tightly fits or contacts a contact member such as a layer forming blade, or the like, and wherein the developer carrier is free of image defects when used in an imaging apparatus. The present invention further relates to an imaging apparatus incorporating such developer carriers.
2. Description of the Related Art
In electrophotographic apparatuses or electrostatic recording apparatuses such as photocopiers, printers and faxes, elastic members including development rollers, feeder rollers, and conveyor rollers play different roles in electrophotographic processes including development, formation of toner layers, cleaning, and feeding and conveying sheets of paper. These elastic members are required to have different properties combined in balance depending on their applications.
Pressure development is a known imaging technique used in electrophotographic imaging apparatus such as photocopiers and printers in which single component toner is provided to an imaging body, such as a photosensitive body, retaining an electrostatic latent image. The toner attaches to the latent image and visualizes the image. Examples of such imaging methods are known from U.S. Pat. No. 3,152,012 and U.S. Pat. No. 3,731,146. In the pressure development, a toner carrier, i.e., a developer carrier, carrying toner is brought into contact with an imaging body, i.e., a photosensitive body, retaining an electrostatic latent image to allow the toner to attach to the latent image to form an image. This makes it necessary for the toner carrier to be made of electrically conductive, elastic materials.
FIG. 2 is a schematic view showing an example of an imaging apparatus employing the pressure development technique. In the pressure development, as shown in FIG. 2, a developer (toner) carrier 1 (developer roller) is disposed between a developer (toner) applying roller 5 for providing developer (toner) and an imaging body 6 (photosensitive body) retaining an electrostatic latent image. When the toner carrier 1, imaging body 6, and toner applying roller 5 rotate in the direction indicated by the respective arrows in FIG. 2, the toner applying roller 5 applies toner 7 to the surface of toner carrier 1 and the toner is made into a thin, uniform layer by a layer forming blade 8. The toner carrier 1 rotates while remaining in contact with the imaging body 6. This allows the thin-layered toner on the toner carrier 1 to attach to a latent image on the imaging body, visualizing the latent image.
The toner image is transferred onto a recording medium such as sheets of paper in a transfer unit, indicated generally by the reference numeral 9. A cleaning unit, indicated generally by the reference numeral 10, may optionally be arranged. A cleaning blade 11 in the cleaning unit 10 removes the toner remaining on the surface of the imaging body after transfer.
In the imaging apparatus employing the pressure development technique, the toner carrier 1 must rotate while remaining in contact with the imaging body 6.
Accordingly, the toner carrier 1, as shown in the schematic cross-sectional view of FIG. 1, is composed of a shaft 2 made of electrically conductive materials such as metals and an electrically conductive elastic layer 3 formed around the shaft 2. The conductive elastic layer 3 is made of conductive elastic materials, the conductivity of which results from conductive agents blended with an elastic rubber or foam, such as silicone rubber, NBR (acrylonitril-butadiene copolymeric rubber), EPDM (ethylene-propylene-diene copolymeric rubber), polyurethane rubber. Also, a coating layer 4, made of resins or the like, may optionally be disposed on the surface of the conductive elastic layer 3 to control chargeability or adhesiveness with respect to the developer 7, or to control friction with the imaging body 6 or layer forming blade 8, or to protect the photosensitive body from contamination by the elastic body.
Another imaging method is also proposed in which developer carried on a developer carrier is caused to leap directly onto an imaging body including paper leaves such as sheets of paper or OHP paper through port-like control electrodes to form an image. Still another method is proposed in which a thin-layered non-magnetic developer is carried on a surface of a sleeve-like developer carrier which is arranged closely to an imaging body (photosensitive body) without contacting it. The developer is caused to leap onto the photosensitive body to develop an image. An example of such methods is disclosed in Japanese Patent Laid-open Publication No.58-116559.
When toner carriers of the type described above are used in imaging apparatuses, however, lateral lines spaced at a constant cycle may appear on the image, depending on the particular condition in which the imaging apparatus is used. This is considered due to contact marks formed on a surface of the toner carrier upon contact with a contact member such as a layer forming blade. It is known that, in order to reduce the contact marks, the compressive permanent set of an elastic body that forms the toner carrier needs to be lower than a predetermined value.
In the field of the development roller used in photocopiers and printers, there is also a need for rollers that are less susceptible to abrasion than conventional rollers in order to prevent leakage of toner due to rollers abraded in the area contacting a toner sealing member.
Recently, silicone rollers made of silicone-based materials such as silicone rubber have become commonly used as development rollers that are free of the above-mentioned problem associated with roller abrasion. One drawback of these conventional rollers, however, is that, although having solved the problem of roller abrasion, these rollers have an insufficient durability since silicone materials have a relatively low abrasion resistance.